This application claims the priority of German Application No. 10 2004 013 828.1 filed on Mar. 15, 2004, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a yarn withdrawal nozzle for an open-end rotor spinning arrangement comprising a yarn deflecting area and a nozzle throat, in which means for increasing the spinning stability are provided, and in which a spiral-shaped structure is provided in the yarn deflecting area.
Spinning stability often presents a problem in the case of open-end rotor spinning arrangements, as the introduced true yarn twist is not evenly present in the formed yarn end. The introduction of yarn twist takes place mainly between the yarn withdrawal nozzle and the delivery device of the finished yarn. It is often poor in the area between the rotor groove and the yarn withdrawal nozzle. Insufficient twist in this area leads to a low spinning stability, as the binding-in of new fibres in the yarn end no longer functions properly when the reduction in the level of twist falls below a certain value, which in turn results in end breaks. The problem is aggravated in that the form of the yarn withdrawal nozzle has not only a deciding influence on the spinning stability, but also on the yarn quality.
Countless known variations in the design of yarn withdrawal nozzles for open-end rotor spinning arrangements have been made in the past. The optimal yarn withdrawal nozzle, which combines the partly contradictory aims of producing a high yarn quality while simultaneously achieving a good spinning stability, has not yet been found.
A plurality of such known yarn withdrawal nozzles with their advantages and disadvantages are described in the German published patent application 197 38 382 (corresponding U.S. Pat. No. 6,035,625). It is disclosed that “spiral nozzles” produce better yarn values than “notch nozzles”, but achieve a lower spinning stability. As an improvement, a yarn withdrawal nozzle is described which comprises a spiral-shaped surface in the outer area of the funnel-shaped tapering yarn deflecting area, and additional notches in the inner area of the funnel-shaped yarn deflecting area. This embodiment has the disadvantage in that the notches in the yarn deflecting area may damage the yarn very slightly, as the yarn, while it is being deflected at an angle of 90°, is pressed very hard onto the surface of the yarn withdrawal nozzle. In addition, the spiral-shaped structure does not achieve its optimal effect, as it is located only in the outer area of the yarn deflecting area.
A yarn withdrawal nozzle comprising interrupted ribbed structures as well as notches beginning in the yarn deflecting area is known in international patent application WO 03/097911. As a result of the way the yarn is pressed hard onto the nozzle wall, the interruptions of the ribbed structures have almost the same effect as notches. A further disadvantage is that the interruptions are located very far away from the center line of the yarn withdrawal nozzle. The greater the distance of the interruption from the center line, the more aggressive the effect on the yarn, and the quicker yarn damage occurs. At the same rotational speed of the yarn, the pressing onto the nozzle wall due to the centrifugal forces is proportional to the distance from the center line. In addition, the speed of the surface of the nozzle wall, which surface skims past the yarn, is also proportional to the distance from the center line.
German published patent application 42 24 632 (corresponding U.S. Pat. No. 5,423,177) describes a “spiral nozzle”, in which the spiral-shaped structure in the yarn deflecting area is formed by linear surfaces. The aim here is to keep the contact pressure of the deflected yarn to a minimum. In the transition areas of the linear surfaces from one spiral corridor to the next, edges are provided which transfer the forces to the yarn. It is disadvantageous that the edges, when new, are relatively sharped-edged and can thus easily damage the yarn. Furthermore, these sharp edges wear out very quickly, so that the forces transferable to the yarn are of different strengths. If, as provided for sensitive yarns, the edges are rounded from the beginning, then the contour of the funnel-shaped yarn deflecting area is almost comparable to a smooth nozzle. The advantages of a “spiral nozzle” are thus practically no longer present.
The non-generic German published patent application 102 55 723 describes a yarn withdrawal nozzle comprising a coaxial circular structure of bulges and grooves in the yarn deflecting area, as well as notches positioned downstream for a high spinning stability. Here the cost-effective production by means of simple tools is of foremost importance. The advantages of the spiral in the yarn deflecting area are deliberately omitted and lesser yarn values are taken into account.
Supplementary to the structures in the yarn deflecting area of the yarn withdrawal nozzle, balloon-disturbing sleeves, also known as “vortex inserts”, which are arranged downstream of the yarn withdrawal nozzle, are known from German published patent 32 20 402 (corresponding U.S. Pat. No. 4,516,397). These balloon-disturbing sleeves are applied for generating a particularly hairy yarn. These are essentially spinning components which processes the yarn very roughly, as the pulling out of the individual fibers to create the desired hairiness, the formed yarn is damaged to such an extent that the tensile strength and evenness values deteriorates.
Based on the first mentioned publication, it is an object of the present invention to create a further improved yarn withdrawal nozzle which delivers high yarn values together with a high degree of yarn stability.
This object has been achieved in the case of a yarn withdrawal nozzle of the above mentioned type according to certain preferred embodiments of the present invention in that the spiral-shaped structure extends essentially over the entire yarn deflecting area and is designed as a continuous structure without interruptions, and in that in the nozzle throat in yarn withdrawal direction there is another structure directly downstream of the spiral-shaped structure, wherein both structures in the yarn deflecting area and in the nozzle throat comprise rounded bulges and deflecting area and in the nozzle throat comprise rounded bulges and rounded recesses, so that forces are transferred to the yarn by the structures in a way which does not damage the yarn.
Due to the regular waved shape of the structure in almost the entire funnel-shaped yarn deflecting area, the yarn withdrawal nozzle of the present invention possesses the advantage in that a particularly good yarn rest and yarn support is possible even in the highly problematic yarn deflecting area. At the same time, forces arise due to the spiral-shaped structure which have an effect on the yarn and whose height can be easily influenced by the height of the wave-shaped structure. The forces work on the one hand as a thrust component against the withdrawal direction and favor the spread of the twist in the direction of the rotor groove. On the other hand they effect a rolling component around the yarn axis, which effects a rolling of the yarn at the funnel-shaped yarn deflecting area. Thanks to the rolling, long single fibers, standing out from the yarn, are laid down. This effects an improvement in the quality of the yarn, as the long hairs are particularly undesirable in further processing. Furthermore the rolling of the yarn effects a false twist generation, which in turn effects a higher yarn twist in the area between the rotor groove and the yarn withdrawal nozzle. The rolling procedure is supported by the structures in the nozzle throat, as thread tension variations are generated in the yarn. The yarn, rotating in the form of yarn balloon, comes into contact with the walls of the nozzle throat and is put into a twist around its own longitudinal axis by the structures in the nozzle throat. This brings about an increase in spinning stability while at the same time achieving good yarn values. Because the structure in the nozzle throat consists of rounded bulges and recesses, and because the relative speed of the yarn to the nozzle throat walls is low due to a correspondingly small diameter of the nozzle throat, yarn and fibre damage does not occur even at high rotor speeds.
In a further advantageous embodiment of the invention it is provided that the yarn withdrawal nozzle is designed in such a way that it is particularly simple and cost-effective to make. The spiral-shaped structure in the yarn deflecting area is formed without an undercut, so that the yarn withdrawal nozzle can easily be removed from the mould when being made by means of casting or pressing processes.
In order to achieve a long serviceable life, the yarn withdrawal nozzles are made out of a high-performance ceramic. In the case of particularly temperature-sensitive fibre materials such as polyester, it is advantageous to make the yarn withdrawal nozzle, at least in the yarn deflecting area, from steel—for example hardened steel. This ensures good heat transport. In a further embodiment of the present invention it can be advantageous to design the metal yarn withdrawal nozzle with a wear-resistant coating.
In order to increase flexibility it is advantageous to design the yarn withdrawal nozzle as a multi-part component, and to combine various structures in the nozzle throat together with a basic design of the spiral in the yarn deflecting area. Thus different materials can be easily combined according to the requirements regarding heat conductivity and wear resistance.
These and further objects, features and advantages of the present invention will become more readily apparent from the following detailed description thereof when taken in conjunction with the accompanying drawings